The present invention relates to a cathode ray tube, and particularly, but not exclusively, to a display tube having a channel plate electron multiplier and electrostatic beam scanning at the input side of the electron multiplier.
British Patent Specification No. 2101396A discloses such a display tube. Display tubes having channel plate electron multipliers are particularly susceptible to contrast degradation due to electrons being scattered from the input surface of the electron multiplier and entering channels at a point distant from their point of origin. In the case of electrostatically scanned display tubes, particularly flat display tubes, it is not possible to produce a positively biased field at the input side of the electron multiplier to draw-off back-scattered electrons because this would conflict with the field conditions necessary to achieve proper scanning of the incident electron beam, these field conditions being created by deflection electrodes held at the same potential or a more negative potential than the multiplier input.